1. Field of the Invention
This invention relates to a stray light cutting structure for an optical device, and more particularly to a stray light cutting structure which cuts stray light which travels in such a direction as to enter an optical component in the optical device and to be reflected at a side surface thereof.
2. Description of the Related Art
In various optical devices, light reflected at a light transmitting surface of an optical component of the optical device sometimes travels through the device as stray light. For example, in a solid state laser in which an etalon is provided in a Fabry-Perot resonator at an angle to the axis of the resonator as disclosed, for instance, in Japanese Unexamined Patent Publication No. 7(1996)-263785, light reflected at a light transmitting surface of the etalon travels in a direction at an angle to the axis of the resonator.
In a Fabry-Perot resonator, oscillating light travels in parallel to optical axes of optical components such as mirrors forming the Fabry-Perot resonator, and a solid laser crystal and a wavelength convertor element disposed inside the resonator. When the stray light traveling in a direction at an angle to the axis of the resonator interferes with the oscillating light, great fluctuation in output power can occur. The problem in the solid state laser will be described in detail with reference to FIGS. 14A to 14C, hereinbelow.
It is assumed that the solid state laser comprises, as shown in FIG. 14A, a semiconductor laser 10 as a pumping light source, a condenser lens 12 which condenses a laser beam 11 emitted from the semiconductor laser 10, a solid laser crystal 13 which is pumped by the laser beam 11, a resonator mirror 14 disposed forward of the solid laser crystal 13, a wavelength convertor element 15 disposed inside a resonator formed by the resonator mirror 14 and the solid laser crystal 13, a Brewster plate 16 for polarization control and an etalon 17 for oscillating wavelength selection.
In such a solid state laser, light emitted from the solid laser crystal 13 pumped by the laser beam 11 resonates between the rear end face 13a of the laser crystal 13 and the mirror face 14a of the resonator mirror 14, whereby a solid laser beam 18 oscillates. The solid laser beam 18 is converted to its second harmonic 19 by the wavelength convertor element 15 and substantially only the second harmonic 19 emanates from the resonator mirror 14. The Brewster plate 16 controls the direction of polarization of the solid laser beam 18 and the etalon 17 selects the oscillating wavelength (i.e., a longitudinal mode) of the solid laser beam 18.
The reflectance of the etalon 17 has a strong wavelength-dependency and a wavelength to which the phases of reflection of opposite sides of the etalon are reverse to each other and accordingly, the reflectance of the etalon 17 to which is very low is selected, whereby the solid laser beam 18 oscillates at the selected wavelength. The reflectance of the etalon 17 to the solid laser beam 18 is minimized at this time and is evaluated to be about 2%. Since the etalon 17 is inclined by 1xc2x0 to a direction normal to the optical axis of the resonator, stray light which is reflected at the surface of the etalon 17 in a direction at 2xc2x0 to the optical axis of the resonator is generated as indicated 20 in FIG. 14A.
The stray light 20 is reflected in total reflection at a side surface 15a of the wavelength convertor element 15, which may be, for instance, a LiNbO3 crystal having periodic domain reversals, and is further reflected at the rear end face 13a of the solid laser crystal 13 provided with HR (high-reflection) coating as shown in FIG. 14B.
Further, the stray light 20 can be reflected at the surface of the etalon 17 to travel in parallel to the optical axis of the resonator as shown in FIG. 14C. That is, the stray light 20 can travel in the same direction as the solid laser beam 18 (abbreviated in FIGS. 14B and 14C) and can be sometimes superimposed on the solid laser beam 18 within the range thereof to interfere with the solid laser beam 18.
When the stray light 20 interferes with the solid laser beam 18, the state of interference varies depending on the phase state and/or the intensity of the stray light 20, which increases and reduces loss in the resonator. Accordingly, slight stray light 20 can greatly change the output power of the solid state laser. Since the phase state of the stray light 20 changes according to change of strain of optical components and the components holding them, change of temperature of the optical components and the components holding them, and the like, the resonator becomes very instable and the output power of the solid state laser greatly fluctuates according to the state during assembly and/or the time from assembly.
In view of the foregoing observations and description, the primary object of the present invention is to provide a structure for cutting stray light which travels in such a direction as to enter an optical component in the optical device and to be reflected at a side surface thereof.
In accordance with a first aspect of the present invention, there is provided a stray light cutting structure for an optical device provided with an optical component through which a predetermined light beam travels in parallel to the optical axis of the optical device, the structure being for cutting stray light, which travels at an angle to the optical axis of the optical device to enter the optical component through one end face thereof, and comprising
at least one notch formed on one side face of the optical component.
In the stray light cutting structure of the first aspect, the stray light is cut after the stray light enters the optical component.
The notch may be formed only at one place in the longitudinal direction of the side face or at a plurality of places in the longitudinal direction of the side face.
When the notch is formed only at one place in the longitudinal direction of the side face of the optical component, it is preferred that the notch be formed at the middle of the optical component in the longitudinal direction thereof and the depth d1 of the notch satisfies formula d1 greater than (L/2) tan xcex8 wherein xcex8 represents the angle between said one side face of the optical component and the direction of travel of the stray light in the optical component and L represents the length of the optical component.
When the notch is formed at a plurality of (Nxe2x89xa72) places in the longitudinal direction of the side face of the optical component, it is preferred that each of the notches be formed at the middle of each of the areas which are obtained by dividing the side face of the optical component into N equal parts in the longitudinal direction thereof and the depth d1 of each of the notches satisfies formula d1 greater than (1/N)xc2x7(L/2) tan xcex8 wherein xcex8 represents the angle between said one side face of the optical component and the direction of travel of the stray light in the optical component and L represents the length of the optical component.
However the depth d1 of the notch should be limited so that the notch does not interfere with the predetermined light beam which travels in parallel to the optical axis of the optical device.
In the stray light cutting structure of the first aspect of the present invention, the stray light entering the optical component is cut by the notch when the stray light impinges upon the notch on the way to the side face of the optical component or after reflected (e.g., in total reflection) by the side face of the optical component.
In the case where a single notch is formed at the middle of the optical component in the longitudinal direction thereof, light which enters the optical component through one end thereof to be reflected at a part of the side face between said one end and the middle of the side face is all cut by the notch after reflected by the side face, whereas light which enters the optical component through one end thereof to be reflected at a part of the side face between the other end and the middle of the side face is all cut by the notch before reflected by the side face if the depth d1 of the notch satisfies formula d1 greater than (L/2) tan xcex8.
In the case where the notch is formed at a plurality of (Nxe2x89xa72) places in the longitudinal direction of the side face of the optical component and each of the notches is formed at the middle of each of the areas which are obtained by dividing the side face of the optical component into N equal parts in the longitudinal direction thereof, light which enters each of the areas from one end thereof to be reflected at a part of the side face between said one end and the middle of the area is all cut by the notch provided in the area after reflected by the side face, whereas light which enters each of the areas from one end thereof to be reflected at a part of the side face between the other end of the area and the middle of the area is all cut by the notch provided in the area before reflected by the side face if the depth d1 of the notch satisfies formula d1 greater than (1/N)xc2x7(L/2) tan xcex8.
That is, when the notch is provided at a plurality of places, light impinging upon the side face of the optical component at a given angle xcex8 can be cut with a notch of a shorter depth d1 (=1/N) than when the notch is provided at a single place. In other words, when the notch is provided at a plurality of places, light impinging upon the side face of the optical component at a larger angle xcex8 can be cut with a notch of a given depth d1 than when the notch is provided at a single place. This holds even if the notches are formed on the side face of the optical component at irregular intervals.
In accordance with a second aspect of the present invention, there is provided a stray light cutting structure for an optical device provided with an optical component through which a predetermined light beam travels in parallel to the optical axis of the optical device, the structure being for cutting stray light, which travels at an angle to the optical axis of the optical device to enter the optical component through one end face thereof, and comprising
a diffusing surface which is formed at at least one area of the side face of the optical component to diffuse the stray light.
In the stray light cutting structure of the second aspect, the stray light is diffused and cut when the stray light impinges upon the diffusing surface after the stray light enters the optical component.
It is preferred that the diffusing surface be formed by sandblasting, rough abrasion and/or filing.
In accordance with a third aspect of the present invention, there is provided a stray light cutting structure for an optical device provided with an optical component through which a predetermined light beam travels in parallel to the optical axis of the optical device, the structure being for cutting stray light, which travels at an angle to the optical axis of the optical device to enter the optical component through one end face thereof, and comprising
a chamfered portion formed on an edge portion of said one end face of the optical component and/or an edge portion of the other end face of the optical component to refract the stray light.
In the stray light cutting structure of the third aspect, the stray light is cut before the stray light enters the optical component when the chamfered portion is formed on an edge portion of said one end face of the optical component whereas the stray light is cut after the stray light enters the optical component when the chamfered portion is formed on an edge portion of the other end face of the optical component.
The chamfered portion may be formed on only one of the end faces of the optical component or on both the end faces of the optical component. In the former case, the width d2 of the chamfered portion from the side face of the optical component is preferably larger than Lxc2x7tan xcex8, and in the latter case, the width d2 of each of the chamfered portions from the side face of the optical component is preferably larger than (L/2)xc2x7tan xcex8, wherein L represents the length of the optical component.
As described above with reference to FIG. 14C, stray light traveling at an angle to the optical axis of the optical device after reflected in a certain direction at an optical element like an etalon obliquely disposed inside the optical device comes to travel in parallel to the optical axis after reflected a plurality of times when it returns to the optical component in parallel to the certain direction. Accordingly, by forming a chamfered portion on an edge portion of said one end face of the optical component and/or an edge portion of the other end face of the optical component to refract the stray light, stray light which travels toward the optical component in parallel to said certain direction can be cut.
When the chamfered portion is formed on only one of the end faces of the optical component, light which is to enter the optical component through one end face thereof to impinge upon the side face at angle xcex8 and light which impinges upon the side face at angle xcex8 and emanates from the other end face are all refracted by the chamfered portion if the width d2 of the chamfered portion from the side face of the optical component is larger than Lxc2x7tan xcex8.
To the contrast, when the chamfered portion is formed on both the end faces of the optical component, light which is to enter the optical component through one end face thereof to impinge upon the side face at angle xcex8 and light which impinges upon the side face at angle xcex8 and emanates from the other end face are all refracted by the chamfered portion on either of the end faces if the width d2 of each of the chamfered portions from the side face of the optical component is larger than (L/2)xc2x7tan xcex8.
That is, when the chamfered portion is provided on both the end faces of the optical component, light impinging upon the side face of the optical component at a given angle xcex8 can be cut with a chamfered portion of a half width as compared when the chamfered portion is provided on only one of the end faces. In other words, when the chamfered portion is provided on both the end faces of the optical component, light impinging upon the side face of the optical component at a larger angle xcex8 can be cut with a chamfered portion of a given width d2 as compared with when the chamfered portion is provided on only one of the end faces.
In accordance with a fourth aspect of the present invention, there is provided a stray light cutting structure for an optical device provided with an optical component through which a predetermined light beam travels in parallel to the optical axis of the optical device, the structure being for cutting stray light, which travels at an angle to the optical axis of the optical device to enter the optical component through one end face thereof, and comprising
a diffusing surface formed on an edge portion of said one end face of the optical component and/or an edge portion of the other end face of the optical component to diffuse the stray light.
In the stray light cutting structure of the fourth aspect, the stray light is cut before the stray light enters the optical component when the diffusing surface is formed on an edge portion of said one end face of the optical component whereas the stray light is cut after the stray light enters the optical component when the diffusing surface is formed on an edge portion of the other end face of the optical component.
The diffusing surface may be formed on only one of the end faces of the optical component or on both the end faces of the optical component. In the former case, the width d3 of the diffusing surface from the side face of the optical component is preferably larger than Lxc2x7tan xcex8, and in the latter case, the width d3 of each of the diffusing surfaces from the side face of the optical component is preferably larger than (L/2)xc2x7tan xcex8, wherein L represents the length of the optical component.
It is preferred that the diffusing surface be formed by sandblasting, rough abrasion and/or filing.
In the stray light cutting structure of the fourth aspect, stray light which is to enter the optical component through one end face thereof is diffused not to enter the optical component by the diffusing surface formed on said one end face of the optical component and stray light which enters the optical component through one end face thereof and emanates from the other end face of the optical component is diffused by the diffusing surface formed on the other end face of the optical component.
When the diffusing surface is formed on only one of the end faces of the optical component, light which is to enter the optical component through one end face thereof to impinge upon the side face at angle xcex8 and light which impinges upon the side face at angle xcex8 and emanates from the other end face are all diffused by the diffusing surface if the width d3 of the diffusing surface from the side face of the optical component is larger than Lxc2x7tan xcex8.
To the contrast, when the diffusing surface is formed on both the end faces of the optical component, light which is to enter the optical component through one end face thereof to impinge upon the side face at angle xcex8 and light which impinges upon the side face at angle xcex8 and emanates from the other end face are all diffused by the diffusing surface on either of the end faces if the width d3 of each of the diffusing surface from the side face of the optical component is larger than (L/2)xc2x7tan xcex8.
That is, when the diffusing surface is formed on both the end faces of the optical component, light impinging upon the side face of the optical component at a given angle xcex8 can be cut with a diffusing surface of a half width as compared when the diffusing surface is formed on only one of the end faces. In other words, when the diffusing surface is formed on both the end faces of the optical component, light impinging upon the side face of the optical component at a larger angle xcex8 can be cut with a diffusing surface of a given width d3 as compared with when the diffusing surface is formed on only one of the end faces.
In accordance with a fifth aspect of the present invention, there is provided a stray light cutting structure for an optical device provided with an optical component through which a predetermined light beam travels in parallel to the optical axis of the optical device, the structure being for cutting stray light, which travels at an angle to the optical axis of the optical device to enter the optical component through one end face thereof, and comprising
a light absorption film provided on an edge portion of said one end face of the optical component and/or an edge portion of the other end face of the optical component to absorb the stray light.
In the stray light cutting structure of the fifth aspect, the stray light is cut before the stray light enters the optical component when the light absorption film is provided on an edge portion of said one end face of the optical component whereas the stray light is cut after the stray light enters the optical component when the light absorption film is provided on an edge portion of the other end face of the optical component.
The light absorption film may be provided on only one of the end faces of the optical component or on both the end faces of the optical component. In the former case, the width d4 of the light absorption film from the side face of the optical component is preferably larger than Lxc2x7tan xcex8, and in the latter case, the width d4 of the light absorption film on each end face from the side face of the optical component is preferably larger than (L/2)xc2x7tan xcex8, wherein L represents the length of the optical component.
It is preferred that the light absorption film be at least one of metal film deposited thereon, metal film bonded thereto and an adhesive film for holding the optical component.
In the stray light cutting structure of the fifth aspect, stray light which is to enter the optical component through one end face thereof is absorbed by the light absorption film provided on said one end face of the optical component and stray light which enters the optical component through one end face thereof and emanates from the other end face of the optical component is absorbed by the light absorption film on the other end face of the optical component.
When the light absorption film is provided on only one of the end faces of the optical component, light which is to enter the optical component through one end face thereof to impinge upon the side face at angle xcex8 and light which impinges upon the side face at angle xcex8 and emanates from the other end face are all absorbed by the light absorption film if the width d4 of the light absorption film from the side face of the optical component is larger than Lxc2x7tan xcex8.
To the contrast, when the light absorption film is provided on both the end faces of the optical component, light which is to enter the optical component through one end face thereof to impinge upon the side face at angle xcex8 and light which impinges upon the side face at angle xcex8 and emanates from the other end face are all absorbed by the light absorption film on either of the end faces if the width d4 of each of the light absorption film from the side face of the optical component is larger than (L/2)xc2x7tan xcex8.
That is, when the light absorption film is provided on both the end faces of the optical component, light impinging upon the side face of the optical component at a given angle xcex8 can be cut with a light absorption film of a half width as compared when the light absorption film is provided on only one of the end faces. In other words, when the light absorption film is provided on both the end faces of the optical component, light impinging upon the side face of the optical component at a larger angle xcex8 can be cut with a light absorption film of a given width d4 as compared with when the light absorption film is provided on only one of the end faces.
In accordance with a sixth aspect of the present invention, there is provided a stray light cutting structure for an optical device provided with an optical component through which a predetermined light beam travels in parallel to the optical axis of the optical device, the structure being for cutting stray light, which travels at an angle to the optical axis of the optical device to enter the optical component through one end face thereof, and comprising
a light-shielding member provided near an edge portion of said one end face of the optical component and/or an edge portion of the other end face of the optical component to cut the stray light.
In the stray light cutting structure of the sixth aspect, the stray light is cut before the stray light enters the optical component when the light-shielding member is provided near an edge portion of said one end face of the optical component whereas the stray light is cut after the stray light enters the optical component when the light-shielding member is provided near an edge portion of the other end face of the optical component.
The light-shielding member may be provided on only one of the end faces of the optical component or on both the end faces of the optical component. In the former case, the width d5 of the light-shielding member from the side face of the optical component is preferably larger than Lxc2x7tan xcex8, and in the latter case, the width d5 of each light-shielding member from the side face of the optical component is preferably larger than (L/2)xc2x7tan xcex8, wherein L represents the length of the optical component.
It is preferred that the light-shielding member be formed to double as a means for holding the optical component.
In the stray light cutting structure of the sixth aspect, a light-shielding member provided near the end face (apart therefrom) cuts the stray light in place of the light absorption film in the fifth embodiment and also in the stray light cutting structure of the sixth aspect, a similar effect can be obtained.
When the light-shielding member is provided on only one of the end faces of the optical component, light which is to enter the optical component through one end face thereof to impinge upon the side face at angle xcex8 and light which impinges upon the side face at angle xcex8 and emanates from the other end face are all cut by the light-shielding member if the width d5 of the light-shielding member from the side face of the optical component is larger than Lxc2x7tan xcex8.
To the contrast, when the light-shielding member is provided on both the end faces of the optical component, light which is to enter the optical component through one end face thereof to impinge upon the side face at angle xcex8 and light which impinges upon the side face at angle xcex8 and emanates from the other end face are all cut by the light-shielding member on either of the end faces if the width d5 of each of the light-shielding member from the side face of the optical component is larger than (L/2)xc2x7tan xcex8.
That is, when the light-shielding member is provided on both the end faces of the optical component, light impinging upon the side face of the optical component at a given angle xcex8 can be cut with a light-shielding member of a half width as compared when the light-shielding member is provided on only one of the end faces. In other words, when the light-shielding member is provided on both the end faces of the optical component, light impinging upon the side face of the optical component at a larger angle xcex8 can be cut with a light-shielding member of a given width d5 as compared with when the light-shielding member is provided on only one of the end faces.
Any of the stray light cutting structures described above is preferably applied to a case where the optical device is a laser resonator and the optical component is that disposed inside the laser resonator such as a solid laser crystal or a wavelength convertor element described above.
In this case, the output power of the solid state laser is prevented from greatly fluctuating under the influence of the stray light generated by reflection at an etalon or the like.
Further, any of the stray light cutting structures described above is preferably applied to a case where the stray light is light reflected at an optical component disposed inside a laser resonator. Such an optical component may be, for instance, an etalon described above.
Further, any of the stray light cutting structures described above is preferably applied to a case where the angle of incidence (=90xc2x0xe2x88x92xcex8) of the stray light to the side face of the optical component is an angle which satisfies the condition of total reflection.
When the angle of incidence (=90xc2x0xe2x88x92xcex8) of the stray light to the side face of the optical component is an angle which satisfies the condition of total reflection, the stray light is reflected in total reflection at an interface between the side face and air. In such a case, the intensity of the stray light is kept high and accordingly, it is preferred that the stray light be cut by the stray light cutting structure of this invention to suppress an adverse effect on an optical device which is apt to be affected by intense stray light.